<!DOCTYPE html>
<html>
<head>
<title>Title of the document</title>
<style>
ol {
list-style-type: none;
counter-reset: item;
margin: 0;
padding: 0;
}
li {
display: table;
counter-increment: item;
margin-bottom: 0.6em;
}
li:before {
content: counters(item, ".") ". ";
display: table-cell;
padding-right: 0.6em;
}
li li {
margin: 0;
}
li li:before {
content: counters(item, ".") " ";
}
</style>
</head>
<body>
<ol>
<li>Element 1
<ol>
<li>Sub element 1</li>
<li>Sub element 2</li>
<li>Sub element 3</li>